Screen fabric for making forming wires for paper machines



Nov. 9, 1965 K. u. SCHUSTER 3,216,893

SCREEN FABRIC FOR MAKING FORMING WIRES FOR PAPER MACHINES Filed June 22, 1962 2 Sheets-Sheet 1 FIG 2 PIC-7.

ili llfl' lw Nov. 9, 1965 K. u. SCHUSTER SCREEN FABRIC FOR MAKING FORMING WIRES FOR PAPER MACHINES 2 Sheets-Sheet 2 Filed June 22, 1962 United States Patent 3,216,893 SCREEN FABRIC FOR MAKING FORMING WIRES FOR PAPER MACHINES Karl Ulrich Schuster, Ulmerplatz 1, Giengen/Brenz, Baden-Wurttemberg, Germany Filed June 22, 1962, Ser. No. 204,389 Claims priority, application Germany, July 6, 1961, Sch 29,951 6 Claims. (Cl. 162-348) The present invention relates to a screen fabric for making forming wires for paper machines.

Such forming Wires, that is, both the warp and weft thereof, usually consist entirely of bronze or tombac wire. They have the great disadvantage that they wear out very quickly when in use and that especially in highspeed paper machines they usually last no longer than a few days.

In order to increase the durability of such forming wires, it has already been proposed to make either only the weft wires or both the warp and weft wires of a flexible plastic. However, such plastic forming wires lack the requisite stability. They draw together toward the longitudinal center of the netting because of the elasticity especially of the weft wires, but also of the warp wires, with the result that the forming wire decreases in width and that the connection between the plastic weft wires and the warp wires loosens and the Warp wires lose their uniform spacing from one another. There are also forming wires known in which the warp consists of flexible wire of plastic and the weft entirely of metal wire. However, since the metallic weft wires of such a forming wire are only bent very slightly at the intersections with the plastic warp wires, the latter are not securely held in place and may easily shift when in use. The mesh size of the forming wire then becomes nonuniform with the result that the water cannot drain off uniformly from the paper web and the surface of the latter upon which the forming wire is slightly impressed will .be uneven and unsatisfactory. In addition, the fabric of the forming wire also becomes distorted diagonally with respect to the warp and weft.

It has also been proposed to make the warp and weft or only the weft of forming wires of plastic wire which is provided with a metal core. Such forming wires are, however, not only too expensive, but they also have the disadvantage, especially when they are tightly woven, that at one point or another the plastic covering will be easily torn oif the metal core, which may already occur during the weaving of the fabric but especially when the forming wire is in use. Furthermore, since each wire of such a fabric has usually an outer diameter of only a fraction of a millimeter, the metal core thereof must be so extremely thin that it can no longer possess an adequate stability and cannot confer an increased stability to the plastic covering. It is also obvious that it is extremely difiicult to coat such thin metal cores with plastic as uniformly as required.

It is an object of the present invention to provide a screen fabric for forming wires for paper machines which possesses the advantageous properties of a fabric of a forming wire which is made entirely of plastic but avoids the above-mentioned disadvantages of such a forming wire, and which consists of a resistant fabric which maintains its shape when in use, does not become distorted diagonally, the warp and weft wires of which will not shift relative to each other, and which will retain its original width until it is worn out completely.

According to the invention, this object is attained by making the weft of the screen fabric for the forming wire alternately of metal wire and plastic wire. This produces the advantage that, because of the rigid metal weft wires,

the fabric when in use will not deviate from its original width and cannot yield to the elastic tension of the plastic weft wires. Furthermore, the plastic weft wires which are more sharply bent than the metal weft wires at the intersections with the warp wires prevent the latter from shifting laterally since the warp wires are primarily clamped between the elastic wires of plastic. The entire fabric is therefore very stable against distortion and does not lose its original shape, although it is much more pliant, lighter in weight, and more resistant to mechanical wear than the fabric for forming wires which only consists of metal wire. The alternation of metal weft wires and plastic weft wires also permits the warp wires to be woven-in in the same manner as is known in making forming wires purely of metal wire, namely, transverse to the weaving direction and in an undulating fashion by lateral reciprocating movements of the sley or reed.

As regards the warp of the new forming-wire fabric, there are three dilferent possibilities. It may either consist entirely of plastic wires or entirely of metal wires or alternately of metal wires and plastic wires, although preferably it is made entirely of plastic wires because of the greater resistance of this material to wear, its lower weight, and greater flexibility. When the forming wire is in use, the warp wires thereof are not subjected to any tensile stresses. Because of the alternating shedding in the loom, they apply themselves uniformly around the weft wires and are thereby quite sharply bent regardless of whether they consist of metal or plastic. In forming wires for paper machines it is important that the humps in the bends of the warp wires all lie within the same plane so that the paper web will be provided with a smooth surface and all of the warp wires on the lower side of the forming wire will engage uniformly with the usual couch, breast and table rolls and suction means. Since the plastic weft wires are more flexible than the metal weft wires and the latter are therefore bent over the warp wires less than the plastic weft wires when the fabric is woven on the loom, the humps which are formed on the warp wires would normally--if the metal and plastic weft wires are of an equal diameter-lie slightly higher within the fabric at the intersections with the metal weft wires than at those with the plastic weft wires.

In order to overcome this deficiency and to insure that the humps of the warp wires ,will lie at all intersections within a common plane, the invention further provides that the plastic weft wires are made of a slightly greater diameter than the metal weft wires, namely, by an amount which is proportionate to the sharper bend of the plastic weft wires as compared with the smoother bend of the metal weft wires. The difference in diameter depends upon the properties of the particular plastic weft wire used, and especially upon its flexibility. In general, the plastic weft wire which is employed according to the invention will have a diameter which is about 7 to 9% greater than that of the metal weft wire.

As previously indicated, the warp wires may all be made either of metal or of plastic or alternately of metal and plastic.

Both the metal and plastic wires which are to be used for making the forming-wire fabric according to the invention may be made of the same or similar materials of which such fabrics have previously been made and in particular, the plastics to be used may be of any suitable kind which has an adequate solidity and flexibility.

The features of the invention will become more clearly apparent from the following description of two preferred embodiments thereof which are illustrated in a greatly enlarged scale in the accompanying drawings, in which:

FIGURE 1 shows a plan view of 'a fabric according to the invention with warp wires of plastic;

FIGURE 2 shows a cross section taken along the line II-II of FIGURE 1;

FIGURE 3 shows a cross section taken along the line III-III of FIGURE 1;

FIGURE 4 shows a cross section taken along the line IVIV of FIGURE 1;

FIGURE shows a plan view of a fabric according to the invention with warp Wires of metal;

FIGURE 6 shows a cross section taken along the line VIVI of FIGURE 5;

FIGURE 7 shows a cross section taken along the line VIIVII of FIGURE 5; while FIGURE 8 shows a cross section taken along the line VIIIVIII of FIGURE 5.

The fabric according to the invention which is primarily intended for making forming wires for paper machines consists according to FIGURES 1 to 4 of warp wires 1 of plastic and weft wires which alternately consist of metal wire 2 and plastic wire 3. As illustrated particularly in FIGURE 2, the warp wires 1 are uniformly and sharply bent, while a comparison of FIGS. 3 and 4 shows that the bends 4 of the metal weft wires 2 are smoother than the bends 5 of the plastic weft wires 3. Since the plastic weft wires 3 have a greater diameter than the metal Wires, the humps 6 of the warp-wiresl at their intersections with the plastic weft wires 3 have the same height as the humps 7 of the plastic warp wires 1 at their intersections with the metal weft wires 2.

The fabric according to FIGURES 5 to 8 is provided with warp wires 9 of metal and of weft wires which, as in FIGURES l to 4, consist alternately of metal wires 10 and plastic wires 11. The plastic weft Wires 11 again have preferably a greater diameter than the metal weft wires 10. The bends of the weft wires of this fabric are sharper than those of a fabric with warp wires of plastic, whereas the metal warp wires are more smoothly bent. However, since the plastic weft wires have also in this case a greater diameter than the metal weft Wires, the humps 6 and 7 also lie within the same plane. This compensation in height is especially of importance if the fabric is used as a forming wire for a paper machine.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims,

Having thus fully disclosed my invention, what I claim 1. A screen fabric for making forming wires for paper machines having warp and weft wires, said weft wires consisting alternately of metal and of plastic, and the diameter of the plastic weft wires being greater than the diameter of the metal Weft Wires.

2. A screen fabric for making forming wires for paper machines having warp and weft wires, said weft wires consisting alternately of metal and of plastic, and the diameter of the plastic weft wires being about 7 to 9% greater than the diameter of the metal weft wires.

3. For use as forming wires in a paper-making machine, a screen fabric having warp and weft wires, said weft wires consisting alternately of metal and of plastic, said plastic weft wires being bent around the warp wires to a greater degree than said metal weft wires are bent around said warp wires, said plastic weft wires being of a slightly greater diameter than the metal weft wires so as to raise the humps of the warpwires where they cross said plastic weft wires to the plane of the humps of said warp wires where they cross said metal weft wires, whereby all of the humps formed by the warp wires substantially lie in a common plane, said wires being uniformly spaced so as to constitute said screen fabric a sieve of substantially uniform mesh.

4. For use as forming wires for paper-making machines, a screen fabric as set forth in claim 3 wherein said warp wires comprise plastic wires.

5. For use as forming wires for paper-making machines, a screen fabric as set forth in claim 3 wherein said warp wires comprise metallic wires.

6. For use as forming wires for paper-making machines, a screen fabric as set forth in claim 3 wherein said warp wires consist alternately of plastic wires and metal wires.

References Cited by the Examiner UNITED STATES PATENTS WILLIAM J. STEPHENSON, Primary Examiner. NEDWIN BERGER, Examiner. 

1. A SCREEN FABRIC FOR MAKING FORMING WIRES FOR PAPER MACHINES HAVING WARP AND WEFT WIRES, SAID WEFT WIRES CONSISTING ALTERNATELY OF METAL AND OF PLASTIC, AND THE DIAMETER OF THE PLASTIC WEFT WIRES BEING GREATER THAN THE DIAMETER OF THE METAL WEFT WIRES. 